The Simple Object Access Protocol (SOAP)

1. The Simple Object Access Protocol (SOAP) Ted Huffmire October 17, 2003

2. SOAP • An application of the XML specification • Relies on XML Schema, XML Namespaces • www.w3c.org • Platform independent • Provides a standard way to structure XML Messages

3. XML Message Application Application Discovery Description Packaging Transport Network

4. It is necessary to define: • The types of information to be exchanged • How to express the information as XML • How to send the information

5. SOAP Envelope SOAP Header Header block Header block SOAP Body Message Body SOAP Messages • Header contains blocks of information regarding how to process the message: • Routing and delivery settings • Authentication/authorization assertions • Transaction contexts • Body contains actual message to be delivered and processed

6. Purchase order in document-style SOAP <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Header> <m:transaction xmlns:m=“soap-transaction” s:mustUnderstand=“true”> <transactionID>1234</transactionID> </transaction> </Header> <s:Body> <n:purchaseOrder xmlns:n=“urn:OrderService”> <from><person>Christopher Robin</person> <dept>Accounting</dept></from> <to><person>Pooh Bear</person> <dept>Honey></dept></to> <order><quantity>1</quantity> <item>Pooh Stick</item></order> </n:purchaseOrder> </s:Body> </s:Envelope>

7. RPC Messages Request Message Soap Client Soap Server Response Message

8. RPC-style SOAP Message public Float getQuote(String symbol); <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Header> <m:transaction xmlns:m=“soap-transaction” s:mustUnderstand=“true”> <transactionID>1234</transactionID> </m:transaction> </s:Header> <s:Body> <n:getQuote xmlns:n=“urn:QuoteService”> <symbol xsi:type=“xsd:string”> IBM </symbol> </n:getQuote> </s:Body> </s:Envelope>

9. SOAP response <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Body> <n:getQuoteResponse xmnls:n=“urn:QuoteService”> <value xsi:type=“xsd:float”> 98.06 </value> </n:getQuoteResponse> </s:Body> </s:Envelope>

10. SOAP Faults <s:Envelope xmlns:s=“…”> <s:Body> <s:Fault> <faultcode>Client.Authentication</faultcode> <faultstring>Invalid credentials</faultstring> <faultactor>http://acme.com/</faultactor> <details> <!-- application specific details></details> </s:Fault> </s:Body> </s:Envelope>

11. Standard SOAP Fault Codes • Version Mismatch • MustUnderstand: specify which header blocks were not understood • Server: error can’t be directly linked to the processing of the message • Client: there is a problem in the message (e.g. invalid authentication credentials)

12. Misunderstood header <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Header> <f:Misunderstood qname=“abc:transaction” xmlns:=“soap-transactions” /> </s:Header> <s:Body> <s:Fault> <faultcode>MustUnderstand</faultcode> <faultstring>Header(s) not understood</faultstring> <faultactor>http://acme.com/</faultactor> </s:Fault> </s:Body> </s:Envelope>

13. SOAP Message Exchange Model • SOAP intermediary, or actor, sits between a service consumer and provider and adds value or functionality to the transaction • The set of intermediaries that the message travels through is called the message path • No standard way of expressing the message path • “targeting:” SOAP has a mechanism for identifying which parts of the SOAP message are intented for processing by specific actors in its message path • Only for header blocks: targeted to a specific actor on its message path by using “actor” attribute

14. Intermediary example 1) Submit signed P.Order Buyer Purchasing service 2) Validate signature 3) Process the P.Order Signature validation service

15. The actor header <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Header> <x:signature actor=“uri:SignatureVerifier”> … </x:signature> <s:Body> <abc:purchaseOrder>…</abc:purchaseOrder> </s:Body> </s:Envelope>

16. Microsoft SOAP Routing Protocol <s:Envelope xmlns:s=http://www.w3.org/2001/06/soap-envelope> <s:Header> <m:path xmlns:m=http://schemas.xmlsopa.org/rp/ s:mustUnderstand=“true”> <m:action>http://www.im.org/chat</m:action> <m:to>http://D.com/some/endpoint</m:to> <m:fwd> <m:via>http://B.com</m:via> <m:via>http://C.com</m:via> </m:fwd> <m:from>mailto:johndoe@acme.com</m:from> <m:id>uuid:849bfs-33fb-4a81-b02b-5b7650549dac16</m:id> </m:path> </s:Header> <s:Body> </s:Body> </s:Envelope>

17. SOAP’s Data Encoding • Method of serializing the data intended for packaging • Rules outline how basic application data types are to be mapped and encoded into XML • A simple type system that is a generalization of the common features found in type systems in programming languages, databases, etc. • Rules can be applied in nearly any programming environment • Encoding styles are completely optional and not always useful.

18. Data Encoding Terminology • “value:” represents a single data unit or combination of data units • “accessor:” represents an element that contains or allows access to a value • <firstname>Joe</firstname> • “firstname” is an accessor; “Joe” is a value.

19. Compound Values • A compound value represents a combination of two or more accessors grouped as children of a single accessor • <name> • <firstname>Joe</firstname> • <lastname>Smith</lastname> </name>

20. Compound Values • Two types of compound values: structs and arrays • A struct is a compound value in which each accessor has a different name • <person> • <firstname>Joe</firstname> • <lastname>Smith</lastname> </person>

21. Compound Values • An array is a compound value in which the accessors have the same name. • <people> • <person name=‘joe smith’ /> • <person name=‘john doe’ /> </people>

22. Multifererenced accessor <people> <person name=‘joe smith’> <address href=‘#address-1’> </person> <person name=‘john doe’> <address href=‘#address-1’> </person> </people> <address id=‘address-1’> <street>111 First Street</street> <city>New York</city> <state>New York</state> </address>

23. 3 Methods to express the data type of an accessor: • Use the xsi:type attribute on each accessor, explicitly referencing the data type according to the XML Schema specification: • <person><name xsi:type=“xsd:string”>John Doe</name> • Reference an XML Schema document that defines the exact data type of a particular element within its definition: • <person xmlns=“personschema.xsd”> • <name>John Doe</name></person> • Reference some other type of schema document that defines the data type of a particular element within its definition: • <person xmlns=“urn:some_namespace”> • <name>John Doe</name>

24. SOAP Data Types • Two alternate syntaxes for expressing instances of data types • Anonymous accessor: • <SOAP-ENC:int>36</SOAP-ENC:int> • Anonymous because its name is its type rather than a meaningful id for the value • Named accessor: • <value xsi:type=“xsd:int”>36</value>

25. Arrays • <some_array xsi:type=“SOAP-ENC:arrayType=“se:string[3]”> • <se:string>Joe</se:string> • <se:string>John</se:string> • <se:string>Marsha</se:string> • </some_array>

26. 2D Arrays • <data xsi:type=“SOAP-ENC:Array” SOAP-ENC:arrayType=“xsd:string[2][]”> • <names href=“#names-1”/> • <names href=“#names-2”/> • </data> • <names id=“names-1” xsi:type=“SOAP-ENC:Array” SOAP-ENC:arrayType=“xsd:string[2]”> • <name>joe</name> • <name>john</name> • </names> • <names id=“names-2” xsi:type=“SOAP-ENC:Array” SOAP-ENC:arrayType=“xsd:string[2]”> • <name>mike</name> • <name>bill</name> • </names>

27. Sparse Arrays • <names xsi:type=“SOAP-ENC:Array SOAP-ENC:arrayType=“xsd:string[10,10]”> • <name SOAP-ENC:position=“[2,5]”>data</name> • <name SOAP-ENC:position=“[5,2]”>data</name> • </name>

28. Deployment of Web Service • Listener to receive message • Proxy to take message and translate it into an action to be carried out • Application code to implement that action

29. SOAP Implementations • Apache SOAP for Java • SOAP::Lite for Perl • Microsoft.NET • More: soaplite.com, soaplite.org

30. Handling SOAP methods • Varies with transport layer • Some implement their own HTTP servers • Some expect to be installed as part of a particular web server • HTTP daemon hands the SOAP message to the toolkit’s proxy, which invokes the code • Some support a pluggable transport mechanism • Can select different transport protocols

31. Proxy component • All SOAP toolkits have this • Parses and interprets the SOAP message to invoke the application code • When the proxy component is handed a SOAP message by a listener, it must: • Deserialize the message from XML into native format • Invoke the code • Serialize the response to the message back into XML and hand it back to the transport listener for delivery back to the requester

32. Deploying Web Services • Involves telling the proxy which code to invoke when a particular type of message is received • For example, Apache SOAP uses a deployment descriptor file, which describes the Java class and rules for mapping Java objects used in the service to their XML equivalents

33. SOAP::Lite • Perl-based toolkit • Perl module must be in Perl’s module search path • Available at www.cpan.org

34. Hello Server Example • #Hello.pm – simple Hello module • package Hello; • sub sayHello { • shift; #remove class name • return “Hello “ . Shift; • } • 1;

35. Hello.cgi (cgi script) • #!/usr/bin/perl –w • #hello.cgi – Hello SOAP handler • User SOAP::Transport::HTTP; • SOAP::Transport::HTTP::CGI • -> dispatch_to(‘Hello::(?:sayHello)’) • -> handle • ; • #this script is the glue that ties the listener (HTTP server daemon) to the proxy (SOAP::Lite module).

36. Hello Client: hw_client.pl #!/usr/bin/perl –w # hw_client.pl – Hello Client use SOAP::Lite; my $name = shift; print “\n\nCalling the SOAP Server to say hello\n\n”; print “The SOAP Server says: “; print SOAP::Lite -> uri(‘urn:Example1’) -> proxy(‘http://localhost/cgi-bin/helloworld.cgi’) -> sayHello($name) -> result . “\n\n”;

37. Running the Hello Client • % perl hw_client.pl James • Calling the SOAP Server to say hello • The SOAP Server says: Hello James • %

38. Apache SOAP version of Hello Server • Package samples; • public class Hello { • public String sayHello(String name) { • return “Hello “ + name; • } • }

39. Apache version of Hello Client • import org.apache.soap.*; import org.apache.soap.rpc.*; • public class Example1_client { • public static void main(String[] args) throws Exception { • System.out.println(“\n\nCalling the SOAP Server to say hello\n\n”); • URL url = new URL(args[0]); • String name = args[1]; • Call call = new Call(); • call.setTargetObjectURI(“urn:Example1”); • call.setMethodName(“sayHello”); • call.setEncodingStyleURI( Constants.NS_URI_SOAP_ENC;); • Vector params = new Vector(); • params.addElement(new Parameter(“name”, String.class, name, null)); • call.setParams(params); • System.out.println(“The SOAP Server says: “); • Response resp = call.invoke(url, “”); • if (resp.generatedFault()) { • Fault fault = resp.getFault(); • System.out.println(“\nOuch, the call failed: “); • System.out.println(“ Fault Code = “ + fault.getFaultCode()); • System.out.println(“ Fault String = “ + fault.getFaultString()); • } else { • Parameter result = resp.getReturnValue(); • System.out.println(result.getValue()); • } • } • }

40. Running the Apache client • % java samples.Hello http://localhost/soap/servlet/rpcrouter James • Calling the SOAP Server to say hello • The SOAP Server says: Hello James • %

41. Apache Deployment Descriptor <dd:service xmlns:dd=http://xml.apache.org/xml-soap/deployment id=“urn:Example1”> <dd:provider type=“java” scope=“Application” method=“sayHello”> <dd java class=“samples.Hello” static=“false” /> </dd:provider> <dd:faultListener> org.apache.soap.server.DOMFaultListener </dd:faultListener> <dd:mappings /> </dd:service>

42. Apache SOAP configwuration file • <root> • <dd:service xmlns:dd=http://xml.apache.org/xml- • soap/deployment id=“urn:Example1”> • <dd:provider type=“java” scope=“Application” • methods=“sayHello”> • <dd:java class=“samples.Hello” static=“false” /> • </dd:provider> • <faultListener> • org.apache.soap.server.DOMFaultListener • </dd:faultListener> • <dd:mappings /> • </dd:service> • </root>